#include <bits/stdc++.h>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int n, k, a[5000100];
long long ans;
deque <long long> dq;

int main(){
	in >> n >> k;
	for(int i = 1; i <= n; i++)
		in >> a[i];	
	for(int i = 1; i <= k; i++){
		while(!dq.empty() && a[dq.back()] >= a[i])
			dq.pop_back();
		dq.push_back(i);
	} 	
	ans += a[dq.front()];	
	for(int i = k + 1; i <= n; i++){
		while(!dq.empty() && a[dq.back()] >= a[i])
			dq.pop_back();
		dq.push_back(i);
		while(!dq.empty() && dq.front() < i - k + 1)
			dq.pop_front();
		ans += a[dq.front()];
	}
	out << ans;
	return 0;
}